1. Field of the Invention
The present invention relates generally to a hard disc drive apparatus for driving a hard disc or the like which is employed as an external storage apparatus for a computer and, more particularly, is directed to a tracking servo system, by which a transducer head for reading and writing data is properly positioned on a data track of the hard disc.
2. Description of the Prior Art
A hard disc drive apparatus is employed for driving a hard disc or the like as an external storage apparatus of a computer. According to such a hard disc drive apparatus, data is recorded on concentric tracks formed on the hard disc. Also, sectors of a predetermined number are provided on each track, and data is recorded on and reproduced from each sector. Accordingly, when data is recorded on and reproduced from the tracks of the hard disc, the seeking operation is performed with respect to a track designated a computer, and the data is recorded on and reproduced from the designated sector of the tracks.
FIG. 1 shows a typical recording format of a hard disc 1 according to the prior art. As shown in FIG. 1, the number of data sectors in each track is selected to be constant from the innermost track to the outermost track as shown in FIG. 1. Further, the positions of the boundaries between adjacent data sections are arranged in radial directions. Therefore, it is proposed to provide a servo sector between radially provided data sectors, in which there is sequentially and repeatedly provided servo address data of, for example, 4 bits (00 to 15) in order to perform the track seeking operation. According to this proposal of the sector servo system disc apparatus in which servo address data are repeatedly recorded at every predetermined number of tracks, the upper limit of the head moving speed must be determined in the seeking operation. In the above-mentioned example according to the prior art, the upper limit of the head moving speed is determined such that the head should not cross more than 8 tracks during a period in which the disc 1 is rotated by one sector amount. Thus, a desired track can be detected on the basis of servo address data read intermittently and the position in which the head is positioned.
In the above-mentioned hard disc drive apparatus, however, the lengths of the innermost and outermost peripheral tracks are different by about a factor of two. If the number of sectors in the innermost and outermost peripheral tracks are determined to be constant so that the storage capacity may become constant, then the recording density of the outermost peripheral track will be lowered.
To overcome the above-mentioned defects, a so-called zone recording system is proposed, in which a record surface of the disc is divided dependent on radius positions of the tracks to provide a plurality of zones, and at every zone the number of the data sectors provided in the respective tracks are made different in such a manner that outer zone has more data sectors. According to this proposal, the storage capacity of the whole disc can be increased by substantially twice. However, when the zone recording system is performed in practice, the border positions of the data sectors become irregular in every zone so that a track seeking operation utilizing the servo address data can not be made.
Further, another proposal is known, in which when a plurality of discs are stacked upon use, one surface of a desired disc is employed as a surface in which a servo signal is exclusively recorded, and the track seeking operation is performed by using the servo signal reproduced from this servo signal surface. According to this proposal, one surface of the disc becomes useless for recording and reproducing data, thereby preventing an increase of the storage capacity according to the zone recording system.